Discharge mechanism for shaft kiln

ABSTRACT

A positive displacement volumetric discharge mechanism of the screw auger conveyor type. A series of radially disposed conical screw type augers and underlying retarder plates substantially close the lower end of an annular chamber of a vertical shaft kiln. The augers are rotated to convey solid materials from a bed of such materials in the kiln chamber radially outwardly to an annular discharge throat. The conical augers are formed so that the volume of material conveyed increases with the radial distance from the center of the kiln in order to maintain a constant and uniform downward flow of solid materials throughout out the cross section of the kiln.

United States Patent Hand et al.

both of Denver; Robert K. Harris, Littleton, all of C010.

[73] Assignee: Mintech Corporation, Denver, C010. [22] Filed: Aug. 12,1971 [21] Appl. No.: 171,175

[52] US. Cl ..263/29, 214/18 V, 266/25 [51] Int. Cl ..F27b l/20 [58]Field of Search ..263/29; 266/25; 214/18 V [56] References Cited UNITEDSTATES PATENTS 2,021,991 11/1935 Depew ..214/1sv 3,373,982 3/1968Jones,Jr ..263/29 NOV. 28, 1972 Primary ExaminerJohn J. CambyAttorney-Ralph F. Crandell [5.7] ABSTRACT A positive displacementvolumetric discharge mechanism of the screw auger conveyor type. Aseries of radially disposed conical screw type angers and underlyingretarder plates substantially close the lower end of an annular chamberof a vertical shaft kiln. The augers are rotated to convey solidmaterials from a bed of such materials in the kiln chamber radiallyoutwardly to an annular discharge throat. The conical augers are formedso that the volume of material conveyed increases with the radialdistance from the center of the kiln in order to maintain a constant anduniform downward flow'of solid materials throughout out the crosssection of the kiln.

10 Claims, 7 Drawing Figures 7 PATENIEDHUVZB I972 3.704;O1 l

SHEET 1 OF 4 PATENTEDnnvzelsrz 3 7 04 011 sums or 4 DISCHARGE MECHANISMFOR SHAFT KILN BACKGROUND OF THE INVENTION The field of the invention isthat of discharge mechanisms for vertical circular shaft kilns. Moreparticularly, the invention relates to a discharge mechanism findingparticular, but not necessarily exclusive, use in connection with largediameter vertical shaft kilns of the type adapted for conductingreactions in which the solid reactants have bridging or clinkeringtendencies.

Kilns and furnaces adapted to accommodate a continuous gravity-inducedflow of discreet or particulate solid. materials in exposure to fluids,either gas or liquid, for purposes of carrying out a reaction betweenthe solids and the fluid, have long been known and utilized for theprocessing and treatment of many substances. Appropriately styled shaftkilns, such units are extensively employed in many industrialapplications. In some applications thermal reactions are promoted bymeans of hot gases which flow upwardly in reaction contact with solidmaterials contained y within the kiln. In such processes the efficacy ofthe reaction is, in large measure, determined by the uniformity ofsolids movement through all zones of the kiln, and the uniformity of thegas flow permeating the bed of solids. The shaft kiln or furnaceincludes as a significant factor a mechanism for controlling uniformlythe discharge of solids from the kiln in order to effect a uniform flowrate for all solids moving through the unit.

While some solid materials are relatively free flowing, both before andafter reaction, others, particularly under reaction conditions, tend tocompact or agglomerate into clinker-like bodies, and a bed of suchmaterials can be made to move downwardly through the kiln only withdifficulty. The agglomerating effects become particularly severeadjacent the discharge mechanism. At this point, the agglomeratedmaterials frequently form clinkers or bridges across the dischargemechanism openings thereby effectively closing these openings andpreventing further flow of material through the kiln. The operation mustthen be stopped, the clinkers or bridges removed, and the operationallowed to proceed.

One form of discharge grate is shown in U.S. Pat. No. 3,027,147, issuedMar. 27, 1962 to Lewis H. Brake] and John B. Jones, .lr., for CircularShaft Kiln Discharge Grate. This patent discloses a circular shaft kilndischarge grate embodying circular or annular pusher members adapted fororbital movement between concentric deflector members and subjacentretarder plates. The retarder plates define annular throats underlyingthe deflector members, while the concentric deflector members defineannular throats overlying each of the retarder plates. The pushermembers are positioned between the deflector members and the retarderplates to push material, through the grate mechanism.

A related structure is disclosed in U.S. Pat. No. 3,554,509, issued Jan.12, 1971 to Craig C. Waddle and Robert K. Harris for Discharge Grate ForCircular Shaft Kiln." This patent discloses a discharge grate for acircular shaft kiln, which grate includes a concentric plurality ofcoplanar annular retarder plates defining concentric annular throats. Aplurality of radially extending pusher rods each mounts a series ofannular sector-shaped pusher plates which, when positioned over theannular throats, retard the flow of solids through the grate, and which,upon reciprocation of the rods, move to open the throats and pushmaterial off the edges of the retarder plates. At the same time, the

pusher rods and plates serve to break up any clinkers or agglomeratedmaterials which would tend to bridge across the annular openings andimpede material flow through the kiln.

A conventional cylinder type grate mechanism is shown in U.S. Pat. No.3,101,935, issued Aug. 27,-1963 to Erich Zeltner for Method and Kiln ForBurning Cement, Lime, Dolomite and the Like. The grate mechanismcomprises rotating cylinders formed with a plurality of radiallyextending fingers on a grate shaft. The cylinders are rotated to causethe fingers to break up agglomerates of material formed in the kiln.Free flowing materials, however, would fall through the grate withoutcontrol. 7

Among the problems present in prior art constructions are, as mentionedabove, the discharging from a vertical shaft kiln of materials whichtend to agglomerate or clinker during reaction and tend to bridge acrossgrate discharge mechanism openings. Many of the discharge gratemechanisms known in the prior art are complex structures with attendantmaintenance problems. Many require sliding seals which make themechanisms impractical for-use with high temperature and high pressurereaction systems. It is also desirable that the discharge mechanismprovide for a uniform downward flow of material through the kiln withoutcausing channeling or cavitation resulting from uneven flow of materialsat certain sections or areas of the kiln.

OBJECTS OF THE PRESENT INVENTION The principal object of the presentinvention is to provide an improved positive displacement volumetricdischarge mechanism for a vertical shaft kiln. More particularly, it isan object to provide an improved mechanism which effectively operateswith both particulate free flowing materials and materials which, duringthe kiln reaction, agglomerate to form clinkers or flow-restrictingagglomerates.

Another object of the invention is to provide a grate mechanism of theforegoing character which will afford uniform discharge of solids fromthe kiln without causing channeling or cavitation, and thereby maintaina uniform reaction bed height within the kiln.

- A further object of the present invention is to provide a dischargemechanism of the foregoing character which will operate over a widerange of temperature and pressure conditions.

A more specific object of the invention is to provide a dischargemechanism for vertical shaft kilns which produces a positive volumetricdisplacement without regard to bridging or agglomeration of kiln bedmaterials, and which further provides a relatively constant uniformcontrollable flow rate through the shaft kiln.

Still a further object of the present invention is to provide adischarge grate mechanism which requires a minimum of maintenance, isrugged and long wearing under adverse conditions, is simple to designand operate and is highly effective without regard to the character,particle size or physical characteristic of the material containedwithin the kiln. v

Other objects and advantages of the present invention will becomeapparent from the following description of the invention.

SUMMARY OF THE INVENTION generally annular kiln chamber defined by theouter refractory lined walls of the kiln and an inner refractory linedcolumn. Particulate solid materials are introduced at the top of thekiln and the discharge mechanism is provided for controllablydischarging materials from the bottom of the kiln. The dischargemechanism structure embodies essentially a plurality of conical screwaugers disposed radially in a generally horizontal plane andsubstantially closing the bottom of the annular kiln chamber. The augersare positioned with their apex or inboard ends rotatably journaled onthe center column and their base or outboard ends journaled on the kilnwall. The kiln refractory liner is undercut and overlies the outboardends of the conical augers. A retarder plate structure is positionedbeneath the conical augers to close the annular kiln chamber, butdefines with the outer kiln shell an annular throat through which solidmaterials may be discharged by the conical augers. The augers each areprovided with a spiral rib, and the pitch and spacing of the ribs aresuch I as to accommodate the total quantity of material to be dischargedfrom a point adjacent the inner column. In this manner a uniformvolumetric flow of material is obtained and the general level of solidmaterial in the kiln is maintained at a uniform level. The augers may beconstructed with helical ribs the pitch of which increases from theinboard to the outboard end, or alternatively, the height of whichincreases from the inboard to the outboard end of the auger while thepitch remains constant, or a combination of both. Power means areprovided for continuously, controllably and uniformly rotating theaugers in order to discharge material from the shaft kiln at a selectedcontrolled rate.

DESCRIPTION OF THE DRAWINGS I FIG. 1 is a half-transverse sectionthrough a transversely circular shaft kiln showing in top plan oneillustrative mechanism embodying the present invention.

FIG. 2 is a section axially through the arrangement shown in FIG. 1 withcertain non-essential parts omitted for purposes of clarity.

FIG. 3 is a fragmentary detail section, on a relatively enlarged scale,taken substantially in the plane of line 33 on FIG. 1.

FIG. 4 is a fragmentary view, partially reduced in scale, taken in theplane of line 44 on FIG. 3.

FIG. 5 is a section view taken substantially in the plane of line 5-5 onFIG. 3.

FIG. 6 is a section view, partially reduced in scale, takensubstantially in the plane of line 6-6 on FIG. 3.

FIG. 7 is a diagrammatic representation of a screw auger of the typeshown in FIG. 3 for purposes of illustrating the proportionalconfiguration thereof.

The discharge mechanism shown in the drawings exemplifies the presentinvention and finds particular but not necessarily exclusive use inassociation with transversely circular shaft kilns or furnaces ofmoderate to large diameter for handling materials which tend to compact,agglomerate or bridge during the kiln reaction. The kiln structurecomprises generally an axially vertical tubular shell 20 of appropriaterigid material and of any expedient construction. The kiln constructiondepends primarily upon the reaction to be carried out and the prevailingkiln conditions-The kiln shell 20 is generally provided with anappropriate refractory inner liner 21 which may be formed in one or morelayers of any suitable refractory material. In the kiln constructionembodying the present invention, the kiln is provided with an innercentral column 22 which may be provided with an outer refractory layer23. The reaction chamber 24 defined by the respective refractory layers21, 23 is generally annular in cross section and of a height appropriateto the particular kiln design. Solid particulate reaction materials arefed into the kiln at the top by an appropriate feeding mechanism (notshown) to form a reaction bed, and are discharged from the bottom of thekiln assembly through an appropriate hopper and bulk discharge assembly(not shown). The kiln is supported by a superstructure (not shown) andsuitable conveyor, power and related adjunct equipment is provided as isconventional in the art.

For purposes of providing a positive volumetric control for regulatingthe flow of solid reaction materials through the kilnthe presentinvention contemplates a novel and unobvious discharge mechanismindicated generally by the numeral 30. This mechanism'is constructed notonly to provide for a controlled downward flow of solid reactionmaterials through the kiln, but

also to facilitate the upward flow of fluid reaction materials throughthe moving bed of solids maintained in the kiln by the dischargemechanism 30. Referring to FIG. 2, the interior refractory liner 21 onthe kiln shell 20 terminates, at its lower end at a point closelyadjacent but spaced above the discharge mechanism 30, and defines aninterior overhang or shoulder 25. The shoulder is closely juxtaposedabove the discharge end of the discharge mechanism 30 thereby to preventthe free flow of solid materials through the discharge mechanism. Theamount of overhang required depends primarily upon the angle of reposeof the material being treated in the kiln. The angle of repose of agiven material is the angle from the horizontal of the slope or side ofan imaginary pile on which the material will not rest but will slide offof the pile. It will be appreciated that some materials will have a verylow angle of repose and will flow readily, while other materials willhave a high angle of repose approaching or exceeding Where the materialshave a high angle of repose, there may be a tendency of such materialsto bridge, that is, such materials may not be free flowing but willrequire positive conveying in order to be discharged through the kilngrate mechanism.

In the mechanism of the present invention, the grate I mechanism 30includes a plurality of conically shaped screw conveyors or augers 31radially disposed in coplaner relationship over the kiln cross sectionalarea. Underlying the conical augers 31 is a retarder plate structure 32which positively. prevents the gravity flow of solid materials throughthe kiln. Appropriate power drive means and controls 33 are provided fordriving the conical conveyors to positively and volumetrically dischargematerial over the outer peripheral edge of the retarder plate structure32. Various structural supports including bearings, retarder platesupports, driving mechanism supports and the like are provided inconnection with and as a part of the discharge mechanism.

The screw conveyors or augers 31 form an essential part of the dischargemechanism and are horizontally disposed with the axis of rotationextending radially between the center column 22 and the outer shell 20in such a manner,-as shown in FIG. 1, as to substantially enclose thebottom end of the kiln and prevent the free or gravity flow of solidmaterials therethrough. An illustrative conical conveyor or auger 31 isshown in detail in FIG. 3. Referring more particularly to FIGS. 3, 4, 5,and 6, each conical auger 31 is formed by a generally conical shell 35mounted on a shaft 36. The shaft 36 is journaled at the end thereofadjacent the apex or inboard end of the conical shell 35, in a bearingstructure 38 mounted on the interior surface of the central column 22 ofthe kiln structure. For this purpose the end of the shaft 36 is reducedin diameter as at 39 and extends through the wall of the kiln column 22into the bearing structure 38. The bearing structure comprises a bearingmember or housing 40 mounted by a suitable bracket 41 on the kiln column22. The refractory liner 23 on the column is provided with anappropriate aperture 42 through which the shaft extends.

At its opposite end, that is the end adjacent the large or outboard endor base of the shell 35, the shaft 36 is journaled in a bearing member44 mounted by a suitable mounting support 45 on the exterior wall of thekiln shell 20. Where the kiln reaction may include high temperature orhigh pressure reactions, a rotary seal 46 is provided between the shaft36 and the kiln shell 20. The shaft is rotated by an appropriate drivingmechanism indicated generally at 48 (FIG. 4) which will be described inmore detail below,

The conical augers 31 are positioned in the kiln with their narrow orapex ends adjacent the interior column 22 and their outer large or baseends underlying the lower end or shoulder 25 formed by the refractoryliner 21. If desired, the refractory liner 21 may be shaped withsemi-circular recesses 49 defining the shoulder 25 and closelysurrounding the large or base end of the conical auger 31 as shown inFIG. 6. Alternatively, the interior refractory lining 21 may terminatejust above the large ends of the conical auger structure as shown inFIG. 2. As can be seen from FIG. 1, the conical augers 31 are arrangedto substantially close the lower end of the kiln.

The retarder plate structure 32 underlies the conical augers as well asthe lower end of the refractory liner 21 but terminates short of thekiln shell 20 to form an annular discharge throat 52 adjacent the largeends of the conicalaugers 31 and the kiln shell 20, through which throat52 solid material may be discharged by the conveying action of theconical augers 31. The

discharged material is collected in an appropriate hopper or chutemechanism (not shown) and conveyed out of the kiln system.

The retarder plate structure 32 is formed by a plu-' rality of retarderplate segments 54 which are either integrally or mechanically united andcorresponding in number respectively to the number of auger units 31.Eachretarder plate segment 54 is conically dished or shaped to provide aconcave conical channel which fits around or conforms generally to theadjacent conical auger and is mounted in close juxtaposition therewithas shown in FIG. 5. Each retarder plate segment 54 is braced by aplurality of supporting ribs 55, 56, 57

which strengthen the channel plate segment 54 and prevents warping ordistortion during high temperature reactions. The respective segments 54are joined to adjacent like segments at their upper edges to providejoints 58 as illustrated in FIG. 6. In this manner, the retarder platesegments or sections 54 form a unitary, generally annular, dished orscalloped retarder plate structure 32. I

I The retarder plate segments 54 are mounted in the kiln by suitablemounting structures. To this end, the segments are provided withmounting flanges 59 at their inner end (FIG. 3), which flanges aresecured to mounting brackets 60 secured to the interior kiln column 22.At their outer edges, the retarder plate segments 54 are provided withdepending flange portions 61 which are secured to brackets 62 mounted onthe kiln shell wall 20. Any suitable provision may be made on theretarder plate segments 54 to provide for the discharge throat 52.

For purposes of providing a uniform reaction within the kiln, preventingchanneling and insuring an even, uniform downward flow of materialthroughout the kiln cross section, it is desirable that the discharge orgrate mechanism discharge the solids material uniformly, positively andvolumetrically with respect to the overall cross section of the kiln. Inorder to prevent cavitation, the solids material adjacent the centralcolumn 22 must be discharged at the same rate as the solids materialadjacent the interior surface of the outer refractory liner 21.Expressed another way, the draw-down in the kiln must occur uniformlyover the entire annular cross section. Each particle of material in thebed should travel downwardly at the same rate of speed as any otherparticle anywhere in the kiln at the same elevation. For this purpose,the screw augers 31 transport the material being-discharged from theinnermost perimeter of the annular cross section of the kiln to theoutermost perimeter and thence through the discharge throat 52. Thus, itis required that the conveying capacity of each screw auger 31 increaseat a greater rate from the inboard end to the outboard end than would bethe case if the pitch and depth of the screw flighting on the conicalaxis remained constant.

For conveying purposes, the screw augers 31 are provided with a spiralscrew flight indicated at 65 over the extent of its length. In theembodiment shown, the screw flights are hollow to provide for theconducting of coolant therethrough, as will be described hereinafter.The surface of the conveyor is insulated by a refractory layer 66adjacent and intermediate the screw flights 65.

' sured progressively from the inboard end, that is the small diameterend, to the outboard, that is the large diameter end or base. Both p andd may of course be increased simultaneously to accomplish the desiredresult. On FIG. 7., subscripts are utilized to indicate and distinguishincreasing quantities progressively further from the inboard or smallend of the auger (i.e.-, the right-hand end as shown in FIG. 7). I

The relationship wherein the pitch (p) is progressively increased may beexpressed mathematically as follows:

Equation 1: D =D 2L tan Equation 2:

v L +D) 21r RDd(Dd) Where: g

D diameter of the screw at its origin or inboard end;

D'= diameter of the screw at any point L distance from the origin (shownin FIG. 7 as D,, D D etc.

a distance L,, L L etc. respectively from the origin) 6 angle subtendedby one side of the screw and the center line of rotation;

4) angle subtended by the screw flighting and a plane normal to the axisof rotation (tan qb multiplied by thecircumference, being the pitch (p)of the flighting for one revolution);

v velocity of the bed of material traveling vertically downward in thevessel above the screw, in distance per unit of time;

R rotational speed of the screw in revolutions per unit of time;

d depth of the screw flighting;

L distance from origin along centerline of screw;

Q transport capacity of the screw in quantity per unitof time (volume ofmaterial capable of being rotation, the relationship between the inboardand outboard diameters is expressed as set forth in Equation 1 above.This relationship can be readily observed from FIG. 7.

The projected area (A) of the screw auger, looking downwardly from thetop of the column, may be computed according to the following equation,(which is derived from the equation for determining the area of atrapezoid):

The volume of solidmaterial capable of being transported (Q) at anypoint P, which is a distance L from the origin or apex of the auger, thedistance L being essentially-the distance from the inner column 22 tothe outer or outboard edge of theauger 31, may be computed according tothe following'equation, which expresses the total volume of materialcapable of being transported during a given number of revolutions (R)per unit of time of each auger:

The volume of material (Q) to be transported by an auger must equal thevolume of solid material (V) moving down through the portion of thecolumn directly above the given screw auger in a unit of time. Thisvolume of transported material (V) is computed as follows:

The total transport capacity (Q) must equal the total transportedmaterial (V) at any given point P. There- Rearranging this equation interms of the variable tan Lv(D+D 2R1rm'd 1J'-d This is thus thederivation'of Equation 2 expressed above. By computing the tangent ofthe angle 4) from the above'equation, the pitch of the auger flight atany point P along the auger can be readily determined by multiplying thetangent of the angle (b by the circumference D of the auger at any givenpoint. In this manner, the auger configuration can be readilydetermined. A similar, although somewhat more mathematically complex,formula may be derived fro increasing the height (d), and thus theconveying capacity, of the spiral auger flight from the inboard orsmallend of the convey the sameto the discharge throat 52. The weight of thecolumn on the material adjacent to the augers 31 will force anyagglomerated material into the auger mechanism and the latter willeffectively break up any clumps or agglomerates which may have formedduring I the kiln reaction.

The augers are rotatably driven by a suitable driving mechanism 48. Intheillustrative mechanism shown in the drawings, there is provided aratchet wheel secured to the shaft 36 and defining a plurality ofequally spaced teeth 71. Hydraulically driven dogs or cams 72 engage theratchet teeth 71 and rotate the ratchet wheel, and thereby the shaft 36,at the desired rate. The use of two such hydraulically driven dogs, thehydraulic motors 74 for which are secured to the kiln structure byappropriate brackets 75, provide a relatively continuous rotaryoperation. The use of one such driving dog mechanism will produce asomewhat more intermittent rotation. With the use of two drivingmechanisms, however, one can be driving the ratchet wheel 70 while theother is retracting into position for a subsequent driving operation.Alternatively, electrically driven or hydraulically driven motors andsuitable reducing transmissions may be utilized. It should beappreciated, of course, that relatively high torques will be involved,particularly when the material in the kiln tends to agglomerate andcompact. Thus it is desirable to provide relatively simple yet powerfulmotors for rotating the respective augers.

In the present construction each individual auger 31 is rotatedindividually by 'its own associated driving ratchet mechanism 48. Thisenables the kiln operator to make adjustments to the rate of rotation ofeach auger 31 depending upon the flow of material through the kiln. Oncethe mechanism has been set, little attention is required except whereone screw auger becomes jammed or inoperative, in which case itsparticular driving motor may be shut down. It has been observed that oneor more such augers may be shut down without adversely affecting theflow of materials through the kiln.

The spiral screw flights 65 may either be solid, or as mentioned above,may be hollow to provide for the circulation of coolant therethrough.The latter construction is utilized for kiln configurations in whichhigh temperature reactions are to be conducted. For such purposes,provision is made for circulating a coolant through the entire augerstructure. To this end, the auger shaft 36 is hollow providing aninternal passage 80 and there is positioned axially within said passageacoolant inlet conduit 81. The conduit 81 communicates with an externalcoolant supply conduit 82 while the internal passage 80 of the shaftserves as the outlet passage and communicates through a rotary sealstructure 83 with an outlet conduit 84. The inlet conduit 81 extendsaxially through the shaft 36 into close proximity with the bearingsupporting end 39 thereof so that coolant which flows through theconduit 81 is directed into the bearing end of the shaft to cool thesame. The inlet conduit 81 is supported within the shaft 36 by abulkhead 85 which also serves as a barrier preventing the direct flow ofcoolant from the inlet conduit 81 into the outlet passage 80. Thebarrier 85 thus defines an interior end chamber 86 within the hollowshaft 36.

Coolant flows from the end chamber 86 outwardly from the shaft throughappropriate apertures 88 in the wall thereof into a chamber 89 definedat the inboard or apex end of the auger shell 35. From this chamber 89the coolant flows through an aperture 90 into the hollow spiral screwauger flights 65. The flights 65 define a chamber 91 through which thecoolant flows, and as can be seen from FIG. 3, the coolant flows fromthe inboard or apex to the outboard or base end of the shell 35. At somepoint in the last flight there is provided an outlet aperture 92 whichpermits the coolant to flow out of the spiral flights 65 into theinterior chamber 94 defined by the screw shell 35. From the interiorchamber 94 the coolant flows through passages 95 in the hollow shaft 36into the exhaust chamber and thence through the seal 83 to the outletconduit 84.

With the foregoing construction, coolant can be circulated from theinlet conduit 82 through the shaft 36, the spiral flights 65, into theinterior of the auger shell 35, and thence out through the hollow shaftto the outlet conduit 84, thereby providing a thorough and extensivecoolant circulation system. Both the inboard and outboard bearings 38and 44, respectively, are cooled by the flow of the coolant.

Suitable provision may be made for the introduction of reaction fluidsto the kiln. For this purpose the retarder plates'54 underlying eachscrew auger 31 may be perforated, slotted or otherwise vented to providechannels for the introduction of reaction fluids. When the kiln isconstructed for use with hot materials, the retarder plates are alsoappropriately refractory lined or supplied with coolant. v

The dischargemechanism described herein provides a positive volumetricdischarge of the solid material moving downwardly through the kiln. Anytendency of the reaction materials to clinker or bridge is prevented bythe continual grinding action of the screw auger conveyors. The unitthus described is capable of providing continuous downward flow of solidmaterials 1 at a rate dependent upon the rate of rotation of each auger.As pointed out above, even if one or more augers are completely stopped,the remaining augers have been observed to provide sufficient conveyingcapacity to prevent channeling, cavitation and otherwise irregular flowthrough the kiln.

While a certain illustrative discharge mechanism structure has beenshown in the drawings, and described above in considerable detail, itshould be understood that there is no intention to limit the inventionto the specific form and structure disclosed. On the contrary, theintention is to cover all modifications, alternative constructions,equivalents and uses falling within the spirit and scope of theinvention as expressed in the appended claims.

We claim as our invention:

1. A positive displacement volumetric discharge mechanism for thecontrolled discharge of solid materials from a vertical circular shaftkiln defining a kiln chamber which is generally annular in crosssection, said mechanism comprising a plurality of cone-shaped augersradially disposed within said kiln and substantially closing the lowerend of said annular chamber, a retarder plate underlying said augers andhaving an outer peripheral edge defining an annular discharge throatadjacent the outboard ends of said augers,

means for rotating said augers, a spiral rib on each of said augersdefining an auger channel the volume of which increases, from theinboard end of said auger radially outwardly to the outward end of saidauger adjacent said discharge throat, in direct proportion to thecumulative sum of solid material conveyed thereby from the center of thekiln to the discharge throat so that a uniform material level of solidmaterial is maintained within said kiln as solid material is dischargedtherefrom through said throat.

2. A positive displacement volumetric discharge mechanism as defined inclaim 1 wherein said spiral rib defining the auger channel is of uniformheight and of progressively increasing pitch from the inboard end ofsaid auger to the outboard end thereof, thereby defining an augerchannel of volumetrically increasing capacity.

3. A positive displacement volumetric discharge mechanism as defined inclaim 1 wherein said spiral rib is of constant pitch and the height ofsaid rib progressively increases from the inboard end of said auger tothe outboard end thereof thereby defining a solid material conveyingauger channel of progressively increasing volume.

4. A positive displacement volumetric discharge mechanism as defined inclaim 1 wherein said spiral rib defining the auger channel is ofprogressively increassaid augers independently of each other, a spiralrib on each of said augers for moving material contained ing height andprogressively'increasing pitch from the inboard end of said auger to theoutboard end thereof thereby defining an auger channel of volumetricallyincreasing capacity.

5. A positive displacement volumetric discharge mechanism for thecontrolled discharge of solid materials from a vertical circular shaftkiln, said kiln having a shell defining an inner material confining wallspacedly surrounding a central bearing column having an outer materialconfining wall, said inner and outer walls defining a kiln chamber whichis generally annular in cross section, a plurality of cone-shaped augersradially disposed within said kiln and substantially closing the lowerend of the annular chamber thereof, a retarder plate underlying saidaugers and defining with the outer kiln wall an annular dischargethroat, said outer kiln wall overhanging said annular throat and theoutboard end of said cone-shaped augers, means for rotating said augers,a spiral rib on each of said augers defining with said retarder plate asolid material conveying channel from the inboard end of said augerradially outwardly to the outboard end of said auger adjacent saiddischarge throat, with said solid material conveying auger channelhaving a volume which increases progressively from the inboard end ofsaid auger to the outboard end thereof in direct proportion to thecumulative sum of solid material conveyed thereby from the center of thekiln to the discharge throat so that a uniform material level of solidmaterial is maintained within said kiln as solid material is dischargedtherefrom through said throat.

6. A positive displacement volumetric discharge mechanism forcontrollably discharging material from a vertical circular shaft kilnhaving an outer shell with an undercut inner refractory liner thereonand a central support post axially vertical within said kiln therebydefining a generally annular kiln chamber, a plurality of conical augersradially disposed in the lower end of the kiln and each of said augershaving an inboard end supported on the central post and an outboard endsupported in the kiln shell, said augers substantially closing the lowerend of said annular chamber, each of said augers having its outboard endextending radially outwardly below the undercut refractory liner, anannular retarder plate spacedly underlying said augers and having anouter peripheral edge adjacent said kiln shell and defining therewith anannular throat underlying said undercut refractory wall, means forrotating each of auger channel from the inboard end of said augerradially outwardly to the outboard end of said auger adjacentsaid'discharge throat, with said solid material conveying auger channelhaving a volume which increases progressively from the inboard end ofsaid auger to the outboard end thereof in direct proportion to thecumulative sum of solid material conveyed by the auger from the centerof the kiln to the discharge throat so that a uniform material level ofsolid material is maintained within said kiln as solid material isdischarged therefrom through said throat.

7. A positive displacement volumetric discharge mechanism forcontrollably discharging'material from a vertical circular shaft kilnhaving an outer shell with an undercut inner refractory liner thereonand a central support post axially vertical within said kiln therebydefining a generally annular kiln chamber, a plurality of conical augersradially disposed in the lower end of the kiln and substantially closingthe lower end of saidchamber, each of said augers having the largeoutboard end thereof extending radially outwardly below the undercutrefractory liner, an annular retarder plate spacedly underlying saidaugers and having an outer peripheral edge adjacent the kiln shell anddefining therewith an annular throat underlying said undercut refractorywall, an axial trunnion shaft on each end of each conical auger, bearingmeans on said central support post for supporting the trunnion shaft atthe inboard end of each said auger, bearing means on said kiln shellwall supporting the trunnion shaft at the outboard end of each saidauger, the shaft at the outboard end of each said auger extendingoutwardly through the kiln shell wall, driving means external of thekiln and operatively engaged with each said extending shaft end forrotating each said auger, said spiral rib defining with said retarderplate a solid material conveying auger channel from the inboard end ofsaid auger radially outwardly to the outboard end of said auger adjacentsaid discharge throat, with said solid material conveying auger channelhaving a volume which increases progressively from the inboard end ofsaid auger to the outboard end thereof in direct proportion to thecumulative sum of solid material conveyed by the auger from the centerof the kiln to the discharge throat so that a uniform material level ofsolid material is maintained within said kiln as solid material isdischarged therefrom through said throat.

8. A positive displacement volumetric discharge mechanism as defined inclaim 7 wherein said auger is defined by a hollow conical shell closedat each end by an inboard base member and an outboard base memberrespectively, said rib is formed by a channel cooperating with the augershell to define an interior spiral rib conduit, and said auger issupported by a hollow shaft which extends through said inboard andoutboard base plates to define said trunnion shaft portions, the inboardend of said shaft being closed, a conduit extend ing axially throughsaid hollow shaft and terminating in an open end closely adjacent theinboardv end of said shaft, an interior bulkhead within said auger shelladjacent the inboard end thereof and defining an interior chambertherewith, an interior bulkhead within auger shaft adjacent the inboardend thereof and defining an interior chamber therewith, means definingapassage through said inboard end of said auger shaft communicatingbetween said interior chambers, means defining a passage between saidinterior auger chamber and said rib chamber adjacent the inboard end ofsaid auger rib, and means defining a passage through said shaftcommunicating between the outboard end of said auger chamber and saidhollow shaft, means exterior of said kiln for supplying a coolant tosaid shaft conduit, and means for exhausting coolant from said hollowshaft whereby coolant can be circulated through said shaft conduit intosaid inboard chambers and thence through said hollow ribs to said augerchamber and exhausted from said auger chamber through said hollow shaftso that the said auger and rib structure can be cooled during hightemperature operations of said kiln.

9. A positive displacement volumetric discharge mechanism as defined inclaim 7 wherein said annular retarder plate comprises a plurality ofsegments, each segment being conically concave and adapted to partiallysurround an adjacent superposed conical auger, and means on saidsegments for attaching said segments together to define an annularretarder plate structure and for mounting said structure in said annularkiln chamber.

10. A positive displacement volumetric discharge mechanism for thecontrolled discharge of solid materials from a vertical circular shaftkiln defining a kiln chamber which is generally annular in crosssection, said mechanism comprising a plurality of cone-shaped augersradially disposed within said kiln and substantially closing the lowerend of said annular chamber, a

being of uniform height and of progressively increasing pitch from theinboard end of said auger to the outboard end thereof, the pitch angleof the auger rib being determined by the equation the pitch angle L thedistance from the inboard end of the auger along the auger centerline vthe velocity of the bed of solid material traveling verticallydownwardly in the kiln above the auger D the diameter of the auger atits inboard end D= the diameter of the auger at distance L from itsinboard end d= the height of the auger rib R= the rotation speed of theauger said auger thereby defining a solid material conveying augerchannel the volume of which increases progressively in direct proportionto the cumulative sum of solid material conveyed thereby from the centerof the kiln to the discharge throat so that a uniform material level ofsolid material is maintained within said kiln as solid material isdischarged therefrom through said throat.

1. A positive displacement volumetric discharge mechanism for thecontrolled discharge of solid materials from a vertical circular shaftkiln defining a kiln chamber which is generally annular in crosssection, said mechanism comprising a plurality of cone-shaped augersradially disposed within said kiln and substantially closing the lowerend of said annular chamber, a retarder plate underlying said augers andhaving an outer peripheral edge defining an annular discharge throatadjacent the outboard ends of said augers, means for rotating saidaugers, a spiral rib on each of said augers defining an auger channelthe volume of which increases, from the inboard end of said augerradially outwardly to the outward end of said auger adjacent saiddischarge throat, in direct proportion to the cumulative sum of solidmaterial conveyed thereby from the center of the kiln to the dischargethroat so that a uniform material level of solid material is maintainedwithin said kiln as solid material is discharged therefrom through saidthroat.
 2. A positive displacement volumetric discharge mechanism asdefined in claim 1 wherein said spiral rib defining the auger channel isof uniform height and of progressively increasing pitch from the inboardend of said auger to the outboard end thereof, thereby defining an augerchannel of volumetrically increasing capacity.
 3. A positivedisplacement volumetric discharge mechanism as defined in claim 1wherein said spiral rib is of constant pitch and the height of said ribprogressively increases from the inboard end of said auger to theoutboard end thereof thereby defining a solid material conveying augerchannel of progressively increasing volume.
 4. A positive displacementvolumetric discharge mechanism as defined in claim 1 wherein said spiralrib defining the auger channel is of progressively increasing height andprogressively increasing pitch from the inboard end of said auger to theoutboard end thereof thereby defining an auger channel of volumetricallyincreasing capacity.
 5. A positive displacement volumetric dischargemechanism for the controlled discharge of solid materials from avertical circular shaft kiln, said kiln having a shell defining an innermaterial confining wall spacedly surrounding a central bearing columnhaving an outer material confining wall, said inner and outer wallsdefining a kiln chamber which is generally annular in cross section, aplurality of cone-shaped augers radially disposed within said kiln andsubstantially closing the lower end of the annular chamber thereof, aretarder plate underlying said augers and defining with the outer kilnwall an annular discharge throat, said outer kiln wall overhanging saidannular throat and the outboard end of said cone-shaped augers, meansfor rotating said augers, a spiral rib on each of said augers definingwith said retarder plate a solid material conveying channel from theinboard end of said auger radially outwardly to the outboard end of saidauger adjacent said discharge throat, with said solid material conveyingauger channel having a volume which increases progressively from theinboard end of said auger to the outboard end thereof in directproportion to the cumulative sum of solid material conveyed thereby fromthe center of the kiln to the discharge throat so that a uniformmaterial level of solid material is maintained within said kiln as solidmaterial is discharged therefrom through said throat.
 6. A positivedisplacement volumetric discharge mechanism for controllably dischargingmaterial from a vertical circular shaft kiln having an outer shell withan undercut inner refractory liner thereon and a central support postaxIally vertical within said kiln thereby defining a generally annularkiln chamber, a plurality of conical augers radially disposed in thelower end of the kiln and each of said augers having an inboard endsupported on the central post and an outboard end supported in the kilnshell, said augers substantially closing the lower end of said annularchamber, each of said augers having its outboard end extending radiallyoutwardly below the undercut refractory liner, an annular retarder platespacedly underlying said augers and having an outer peripheral edgeadjacent said kiln shell and defining therewith an annular throatunderlying said undercut refractory wall, means for rotating each ofsaid augers independently of each other, a spiral rib on each of saidaugers for moving material contained within said kiln radially outwardlyand discharge the same through said annular throat, said spiral ribdefining with said retarder plate a solid material conveying augerchannel from the inboard end of said auger radially outwardly to theoutboard end of said auger adjacent said discharge throat, with saidsolid material conveying auger channel having a volume which increasesprogressively from the inboard end of said auger to the outboard endthereof in direct proportion to the cumulative sum of solid materialconveyed by the auger from the center of the kiln to the dischargethroat so that a uniform material level of solid material is maintainedwithin said kiln as solid material is discharged therefrom through saidthroat.
 7. A positive displacement volumetric discharge mechanism forcontrollably discharging material from a vertical circular shaft kilnhaving an outer shell with an undercut inner refractory liner thereonand a central support post axially vertical within said kiln therebydefining a generally annular kiln chamber, a plurality of conical augersradially disposed in the lower end of the kiln and substantially closingthe lower end of said chamber, each of said augers having the largeoutboard end thereof extending radially outwardly below the undercutrefractory liner, an annular retarder plate spacedly underlying saidaugers and having an outer peripheral edge adjacent the kiln shell anddefining therewith an annular throat underlying said undercut refractorywall, an axial trunnion shaft on each end of each conical auger, bearingmeans on said central support post for supporting the trunnion shaft atthe inboard end of each said auger, bearing means on said kiln shellwall supporting the trunnion shaft at the outboard end of each saidauger, the shaft at the outboard end of each said auger extendingoutwardly through the kiln shell wall, driving means external of thekiln and operatively engaged with each said extending shaft end forrotating each said auger, said spiral rib defining with said retarderplate a solid material conveying auger channel from the inboard end ofsaid auger radially outwardly to the outboard end of said auger adjacentsaid discharge throat, with said solid material conveying auger channelhaving a volume which increases progressively from the inboard end ofsaid auger to the outboard end thereof in direct proportion to thecumulative sum of solid material conveyed by the auger from the centerof the kiln to the discharge throat so that a uniform material level ofsolid material is maintained within said kiln as solid material isdischarged therefrom through said throat.
 8. A positive displacementvolumetric discharge mechanism as defined in claim 7 wherein said augeris defined by a hollow conical shell closed at each end by an inboardbase member and an outboard base member respectively, said rib is formedby a channel cooperating with the auger shell to define an interiorspiral rib conduit, and said auger is supported by a hollow shaft whichextends through said inboard and outboard base plates to define saidtrunnion shaft portions, the inboard end of said shaft being closed, aconduit extending axially through said hollow shaft and termInating inan open end closely adjacent the inboard end of said shaft, an interiorbulkhead within said auger shell adjacent the inboard end thereof anddefining an interior chamber therewith, an interior bulkhead withinauger shaft adjacent the inboard end thereof and defining an interiorchamber therewith, means defining a passage through said inboard end ofsaid auger shaft communicating between said interior chambers, meansdefining a passage between said interior auger chamber and said ribchamber adjacent the inboard end of said auger rib, and means defining apassage through said shaft communicating between the outboard end ofsaid auger chamber and said hollow shaft, means exterior of said kilnfor supplying a coolant to said shaft conduit, and means for exhaustingcoolant from said hollow shaft whereby coolant can be circulated throughsaid shaft conduit into said inboard chambers and thence through saidhollow ribs to said auger chamber and exhausted from said auger chamberthrough said hollow shaft so that the said auger and rib structure canbe cooled during high temperature operations of said kiln.
 9. A positivedisplacement volumetric discharge mechanism as defined in claim 7wherein said annular retarder plate comprises a plurality of segments,each segment being conically concave and adapted to partially surroundan adjacent superposed conical auger, and means on said segments forattaching said segments together to define an annular retarder platestructure and for mounting said structure in said annular kiln chamber.10. A positive displacement volumetric discharge mechanism for thecontrolled discharge of solid materials from a vertical circular shaftkiln defining a kiln chamber which is generally annular in crosssection, said mechanism comprising a plurality of cone-shaped augersradially disposed within said kiln and substantially closing the lowerend of said annular chamber, a retarder plate underlying said augers andhaving an outer peripheral edge defining an annular discharge throatadjacent the outboard ends of said augers, means for rotating saidaugers, each auger having a spiral rib thereon defining an auger channelof volumetrically increasing capacity from the inboard end of saidaugers radially outwardly to the outboard end of said augers adjacentsaid discharge throat, said ribs being of uniform height and ofprogressively increasing pitch from the inboard end of said auger to theoutboard end thereof, the pitch angle of the auger rib being determinedby the equation where phi the pitch angle L the distance from theinboard end of the auger along the auger centerline v the velocity ofthe bed of solid material traveling vertically downwardly in the kilnabove the auger D the diameter of the auger at its inboard end D'' thediameter of the auger at distance L from its inboard end d the height ofthe auger rib R the rotation speed of the auger said auger therebydefining a solid material conveying auger channel the volume of whichincreases progressively in direct proportion to the cumulative sum ofsolid material conveyed thereby from the center of the kiln to thedischarge throat so that a uniform material level of solid material ismaintained within said kiln as solid material is discharged therefromthrough said throat.